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Growth of the Cretaceous Tuolumne batholith and synchronous regional tectonics, Sierra Nevada, CA: a coupled system in a continental margin arc setting

GROWTH OF THE CRETACEOUS TUOLUMNE BATHOLITH AND
SYNCHRONOUS REGIONAL TECTONICS, SIERRA NEVADA, CA: A COUPLED
SYSTEM IN A CONTINENTAL MARGIN ARC SETTING
by
Valbone Memeti
_____________________________________________________________
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
August 2009
Copyright 2009 Valbone Memeti

Crustal growth at continental margins involves periodic and incremental growth of magmatic arcs, which potentially follow a tempo driven by feedback between tectonic and magmatic processes. Hence, host rock and intruded magma bodies must be studied as an interconnected system. The 95-85 Ma Tuolumne intrusion was emplaced during the Cretaceous Sierra Nevada magma flare-up during regional dextral transpression, which is recorded in both host and plutonic rocks. Preceding intrusion, others hypothesized that miogeocline and overlying Jurassic marine strata were translated into the study area along the Mojave-Snow Lake fault. A field and detrital zircon provenance study shows that these strata are displaced, but not derived from the Mojave Desert as previously proposed, and the place of origin remains uncertain. During growth of the Tuolumne batholith, the incremental rise of magmas was spatially accommodated through downward flow of metamorphic host rock and crystal-magma mush. Magmas forming the major batholith units were derived from isotopically distinct sources and ascended through focused magmatism to form this zoned batholith. However, map patterns, U/Pb zircon geochronology and element and isotope geochemistry of magmatic lobes extending out of this batholith suggest that the batholith had both inward and northwestward growth directions.; While the southern magmatic lobes grew towards the main batholith, the northern lobes grew outward into the metamorphic host rock resulting in the compositionally more primitive southern lobes with simpler zircon populations than in the main batholith. In contrast, the northern lobes sampled the complexity of the main chamber. U/Pb zircon geochronology shows that magmatic lobes were short-lived magma bodies that failed to amalgamate with the main magma chamber. They are thus viewed as snapshots of different stages of batholith construction and the closest to representing individual magma increments. Geochemistry, in combination with field observations, suggests that fractionation crystallization is largely responsible for the compositional variation in the Tuolumne batholith, but is overprinted by longer lasting mixing and recycling processes in the main chamber. This is consistent with the development of large magma chamber(s) at the emplacement level and inconsistent with a dike model that doesn’t allow for extensive magma interactions at the emplacement site.

GROWTH OF THE CRETACEOUS TUOLUMNE BATHOLITH AND
SYNCHRONOUS REGIONAL TECTONICS, SIERRA NEVADA, CA: A COUPLED
SYSTEM IN A CONTINENTAL MARGIN ARC SETTING
by
Valbone Memeti
_____________________________________________________________
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
August 2009
Copyright 2009 Valbone Memeti